Carbon exists in several forms (allotropes) which are significantly different in physical and chemical properties. Carbon can exist in the diamond or graphite crystal forms, as well as several amorphous form, such as coal, coke, carbon black, and charcoal. Carbon can also exist in polymeric forms such as plastic.
Diamond-like carbon (DLC) films comprise a nano-crystalline diamond matrix with polymeric and/or graphite inclusions. Due in part to their hardness, wear resistance, capacity for electrical insulation, and infrared optical properties, DLC films can be used in a wide range of applications including protective coatings for a variety of sensitive surfaces, and infrared anti-reflective coatings on germanium or other suitable materials.
A range of techniques have been developed to deposit DLC films on substrates. For example, radio-frequency (RF) plasma-assisted carbon vapor deposition, sputtering, and ion-beam sputtering have been used. Furthermore, a variety of different carbon-bearing source materials, i.e., solid or gaseous, have also been used in an attempt to provide improved DLC films. However, these techniques may not provide films which exhibit thermal stability, visible transparency, thermal conductance, and hardness approaching that of diamond.
Desirable properties, such as hardness, scratch and wear resistance, high thermal conductivity, visible transmittance, and electrical insulation are generally reduced or even destroyed in a DLC film by the presence of polymeric and/or graphite inclusions. Polymeric inclusions represent defects in the DLC film where carbon-hydrogen bonds exist. Polymeric inclusions can reduce the hardness of a DLC film, reduce heat conduction, and scatter light. Graphite inclusions represent localized islands or regions in the diamond matrix of a DLC film where carbon is in its graphite crystal structure rather than the more ordered diamond crystal structure. Graphite inclusions can reduce the visible optical transparency, the hardness, the thermal conductivity, the mechanical shock resistance, and the electrical breakdown threshold of a DLC film.
As a result, there is a need for films comprising a nano-crystalline diamond matrix that is substantially free of graphite inclusions. There is also a need for methods for depositing the same onto a substrate such that the films may be fabricated at ambient temperature, at low cost, and/or be deposited onto complex substrate shapes.